Method for preparation of transmission electron microscope sample material utilizing sheet mesh

ABSTRACT

A method for processing sample material for use with transmission electron microscopes utilizes a sheet mesh for supporting the sample material during irradiation processing. The sheet mesh is formed of a metallic sheet material having a single opening provided in a central portion thereof, a circumferential edge portion of the opening is tapered from one side of the sheet mesh through to the other and the ankle of the taper corresponds to the ankle of irradiation. Position determining portions are provided on the sheet mesh to assure reliable positioning of the sample material. Also, the method provides a for preparation of the sample material including a protective layer formed over a membrane layer for allowing adhesion of membrane layers made of materials which would otherwise degrade the adhesion layer during processing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a sheet mesh for holdingsamples for examination by TEM (Transmission Electron Microscope).Specifically, the present invention relates to a method of processingsuch sample material utilizing the sheet mesh for supporting thematerial during processing.

2. Description of the Prior Art

For appraising the minute structures of modern semiconductor devices, across-section of the elements of such devices must be examined underhigh magnification, generally by way of a transmission electronmicroscope (TEM) or the like. Referring to FIG. 14 (A)-(D), aconventional method of processing sample material for such a processwill be explained in detail. First, referring to FIG. 14(A), first andsecond substrates 1, 1 have membranes layers 2, 2 applied to one sidethereof respectively. The first and second substrates 1, 1 are arrangedsuch that the membrane layers 2, 2 thereof face each other and arejoined therebetween via an adhesion layer to form a block of samplematerial a. Then, a thin wafer of the sample material a is cut from themain block, such that the membrane layers 2, 2 and the adhesion layer 3run lengthwise substantially through the center of the sample materiala. The sample material a is then attached to a rotatable polishingapparatus 4 via a bonding layer 5. The surface of the sample material ais then exposed to a polishing powder 6 under pressure applied from theopposite side by the rotatable polishing apparatus 4, as seen in FIG.14(B) such that thickness of not more than 20 μm is achieved and bothsides are given a mirror finish.

Then, for processing of the sample material, as seen in FIG. 14(C), thewafer of sample material a is placed over an opening 7a provided in asingle hole mesh 7 (sheet mesh) formed of a metallic sheet material andhaving a thickness of 10 μm, for example. Referring to FIG. 14(D), thesheet mesh 7 with the sample material a thereon is mounted on a rotationapparatus 8 and is then rotated under vacuum conditions while beingirradiated by a high pressure electrical discharge, as for example anAr⁺ ion beam B, at an irradiation angle of 9°-20°. Irradiation iscontinued until a small hole is formed in the center of the wafer ofsample material a, and at this, a finished sample for use with atransmission electron microscope is completed.

According to such conventional processing of sample materials fortransmission electron microscopes, as seen in FIG. 15, when irradiationis carried out, the beam B is reflected by corners and edges of theopenings 7a of the sheet mesh 7. This causes turbulence in the ion flowirradiating the sample material and, as seen in FIG. 16, a circumferenceof the small hole formed in the sample material a may receiveinsufficient irradiation, or unevenness and/or pitting may occur in thefinish of the irradiated surface, degrading sample quality.

Further to this, the efficiency of the adhesion layer 3, used to bindthe sample material a together, is dependent on the qualities of themembrane layers 2, 2. Thus a problem in which sufficient irradiation maynot be obtained due to degradation of the adhesion layer is present.Also, under such conditions, lifting of Al, or another material formingthe sample material a may occur.

Utilizing the above method, examination of an object to be observed by atransmission electron microscope, the membrane layer 2 for example,which must be positioned over the opening 7a of the sheet mesh 7,becomes difficult. Referring to FIG. 17(A) a condition is shown in whichthe positioning of the wafer of sample material a has slipped relativethe surface of the sheet mesh 7 resulting, as seen in FIG. 17(B) ininsufficient irradiation being applied to the portion to be examined,that is the membrane layers 2, 2.

Thus it has been required to provide a method for processing samplematerial for use with transmission electron microscopes in which optimalirradiation characteristics are provided during preparation of samplematerial. Also, a processing method is required in which positioning ofthe sample material is reliably assured and in which the adhesioncharacteristics between layers of the sample material are efficientlymaintained.

SUMMARY OF THE INVENTION

It is therefore a principal object of the present invention to overcomethe drawbacks of the prior art.

It is a further object of the present invention to provide a sheet meshwhich provides optimal irradiation conditions for a sample material andwhich may assuredly position the sample material relative an irradiatingbeam.

It is a further object of the invention to provide a method forprocessing sample material for a transmission electron microscope inwhich adhesion between layers of sample material is efficientlymaintained such that a high level of processing quality may be reliablyassured and peeling of layers of the sample material is prevented.

In order to accomplish the aforementioned and other objects, a methodfor irradiation processing of laminate material used in a semiconductordevice is provided, comprising the steps of: providing first and secondsubstrates, applying a material layer to at least one surface of thefirst and second substrates, applying a protective layer over thematerial layers, joining the material layers of the first and secondsubstrates via an adhesion layer to form a laminate, cutting thelaminate to a predetermined dimension such that the material andadhesion layers form a line substantially through a center thereof,forming an opening between first and second surfaces of a sheet mesh,tapering edge portions of the opening between the first and secondsurfaces at a predetermined irradiation angle, mounting the laminateover the opening on the first surface of the sheet mesh, irradiating thelaminate via an energy beam at the irradiation angle through the openingin the sheet mesh.

According to another aspect of the present invention, a sheet mesh forirradiation processing is provided, comprising: a sheet mesh formounting a sample material for irradiation processing via an energybeam, the sheet mesh having an opening formed through a substantiallycenter portion thereof between first and second opposed surfaces, and, atapered portion formed at edge portions of the opening between the firstsurface and the second surface.

Further, according to still another aspect of the invention, a sheetmesh for transmission electron microscope sample material comprises: asheet mesh capable of holding the sample material for the transmissionelectron microscope at time of polishing via an energy beam, the sheetmesh having an circular opening formed through a substantially centerportion thereof, first and second opposed surfaces, the openingextending from the first surface through the sheet mesh to the secondsurface, the sample material being mountable on the first surface, acontoured portion formed at an edge of the opening circumferentially inan area between the first surface and the second surface such that thesecond surface does not intersect an angle of irradiation by the energybeam.

Yet another aspect of the present invention embodies a method forprocessing sample material for use with a transmission electronmicroscope, comprising the steps of: cutting a portion out of the samplematerial to be used with the transmission electron microscope, mountingthe sample material on a first surface of a sheet mesh, providing anopening in the sheet mesh from the first surface to a second surfaceopposite the first surface, a gradient of an edge portion of the openingbeing formed with a predetermined taper from the first surface to thesecond surface, irradiating the sample material via an energy beamdirected through the opening in the sheet mesh.

A still further embodiment of the principle of the invention may berealized in a sheet mesh for processing sample material for use with atransmission electron microscope, comprising: a metallic sheet meshhaving an opening provided in a substantially center portion thereof,and positioning determining means provided on a side of the sheet meshon which the sample material is to be supported.

The invention may further be realized as a method for processing samplematerial for use with a transmission electron microscope, comprising thesteps of: cutting a portion of the sample material, defining an openingin a layer of sheet mesh, forming a positioning indication on one sideof the sheet mesh, mounting the portion of the sample material on theside of the sheet mesh so as to be set at a predetermined positionindicated by the positioning indication, and irradiating the samplematerial via an energy beam via the opening.

Another method according to the invention for processing sample materialfor use with a transmission electron microscope, comprises the steps of:cutting a portion of the sample material, defining an opening in a layerof sheet mesh, forming a recessed portion on one side of the sheet meshsubstantially around the opening, inserting the portion of the samplematerial into the recessed portion, and irradiating the sample materialvia an energy beam via the opening.

Also according to the invention, a transmission electron microscopesample material is provided, comprising: first and second semiconductorsubstrates, at least one of the substrates having a membrane layerformed thereon, a protective layer formed over the membrane layer, anadhesive layer joining the first and second substrates, the adhesivelayer being adjacent the protective layer.

And, the invention further teaches a method for processing samplematerial for use with a transmission electron microscope, comprising thesteps of: providing first and second substrates, applying an subjectlayer to at least one surface of the first and second substrates,applying a protective layer over the subject layers, joining the subjectlayers of the first and second substrates via an adhesion layer to forma sample, cutting the sample to a predetermined dimension such that thesubject and adhesion layers form a line substantially through a centerthereof, forming an opening between first and second surfaces of a sheetmesh, marking the first surface of the sheet mesh with a positioningindication, mounting the sample over the opening according to thepositioning indications, and irradiating the sample via an energy beamthrough the opening in the sheet mesh.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a cross-sectional view of a composition of sample material fora transmission electron microscope according to the method of theinvention;

FIG. 2 is a cross-sectional view of a composite of sample materialaccording to the method of the invention, wherein an adhesion layer isformed along an axial center of the layer of sample material;

FIG. 3 is a cross-sectional view of a first embodiment of a sheet meshaccording to the processing method for transmission electron microscopesample material according to the invention;

FIG. 4 is a cross-sectional view of the first embodiment showingirradiation processing of the sample material;

FIG. 5 is a cross-sectional view of a modification of a sheet meshportion according to the invention;

FIG. 6 is a cross-sectional view of an alternative modification of asheet mesh portion according to the invention;

FIG. 7 is a cross-sectional view of another modification of a sheet meshportion according to the invention;

FIG. 8 is a cross-sectional view of a still further modification of asheet mesh portion according to the invention;

FIG. 9 is a cross-sectional view of an alternative modification of asheet mesh portion, including a concave portion formed in a firstsurface thereof;

FIG. 10 is a plan view of a second embodiment of a sheet mesh accordingto the method of the invention;

FIG. 11 is a plan view of the sheet mesh of FIG. 10, having a wafer ofsample material positioned thereon;

FIG. 12 is is cross-sectional view of a third embodiment of a sheet meshaccording to the processing method for transmission electron microscopesample material of the invention;

FIG. 13 is a perspective view of the sheet mesh portion of FIG. 12showing a concave portion thereof;

FIGS. 14 A-D show sequential views of a conventional processing methodfor transmission electron microscope sample material including a sheetmesh portion and irradiation apparatus therefor;

FIG. 15 shows conventional irradiation processing according to themethod shown in FIG. 14;

FIG. 18 is a cross-sectional view of sample material after processingaccording to the conventional method of FIGS. 14 and 15; and

FIGS. 17 A and B are cross-sectional views of a conventional processingmethod for transmission electron microscope sample material,illustrating a drawback of the conventional process.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, particularly to FIGS. 1 and 2,preparation of a sample material A for processing according to themethod of the invention will be explained in detail.

As noted above in relation to the conventional process shown in FIGS.14(A) to (D), an efficiency of a adhesion layer 3 utilized to adhere themembrane layers 2, 2 of the sample material A is dependent on thequalities of the membrane layers 2, 2. Thus sufficient irradiation ofthe sample material may not be possible due to degradation of theadhesion layer, or lifting of a material, such as aluminum (Al), oranother material forming the membrane layer 2 of the sample material.

Thus, according to the method of the invention, and as seen in FIG. 1, afine protection layer 14, of SiN, for example, is formed over themembrane layer 2, which is formed on the semiconductive substrate 1. Themembrane layer 2 may be applied by ordinary techniques for constructionof semiconductor devices, and the protection layer 14 may also beapplied according to standard procedures, such as CVD for example.According to the present embodiment, a thickness of the protection layermay be determined at 500 nm, while the thickness of the membrane layer 2may be determined according to a design of the particular semiconductordevice to be examined.

According to the above, and referring now to FIG. 2, two facing samplepieces comprising a semiconductor substrate layer 1, a membrane layer 2and a protection layer 14 are arranged facing each other and adhered bya adhesion layer 3, of epoxy, for example. According to this, theadhesion layer 3 directly binds together the facing protection layers14, 14 of the opposing sample pieces. According to this, membrane layerswhich, according to the conventional method described hereinbefore, itwould not be possible to adhere, may be reliably adhered and thus it ispossible to use membrane layers 2 of such composition as sample materialfor examination under a transmission electron microscope.

Further, although the above described composition of the sample materialA is described optimal for preventing peeling of a membrane layer 2 offaluminum, the method of preparation of sample material according to themethod of the invention is not limited to membrane layers 2 of Al, butof any other material utilized in such application. It will further benoted that, although a protection layer 14 of SiN is taught above, thematerial of the protection layer is not limited to this material, butmay be of any other material selected in view of the composition of themembrane layer 2. Of course, the material of the adhesion layer 3 neednot be limited to epoxy, any other suitable adhesive may also be usedand, although in the above example, a layer of semiconductor substrateis provided on both sides of the sample material A, it may alternativelybe provided on only one side.

Hereinbelow, a structure of a sheet mesh 10 utilized for irradiationprocessing will be described in detail. FIG. 3 shows a cross-sectionalview is shown of a sheet mesh (single hole mesh) 10 having positioned onone surface thereof a wafer of prepared sample material A. At a centerportion of the sheet mesh 10, a circular opening 11 is defined betweenan upper (first) circumferential edge 11a and a lower (second)circumferential edge 11b. For processing, the sample material A ispositioned so as to cover the opening 11 of the sheet mesh 10. Further,a tapered portion 11c is formed circumferentially around an area betweenthe upper edge 11a on which the sample material A is supported and thelower edge 11b. According to the present embodiment, a circumferentialportion 11d of the upper edge 11a of the opening 11 is not tapered and,as seen in FIG. 4, an angle of the tapered portion 11c is determined tobe the same as an angle of an energy beam B, an argon (At) ion beam forexample, utilized for irradiating the sample material. It will also benoted that such a sheet mesh structure as described above is applicablefor processing of conventionally prepared sample material as describedhereinbefore referring to FIGS. 14(A) and 14(B).

As in the conventional process shown in FIG. 14(D), the sheet mesh 10with the sample material A thereon is mounted on a rotation apparatus 8and is then rotated under vacuum conditions while being irradiated bythe energy beam B.

According to the structure of the sheet mesh 10 having the taperedportion 11c formed between edges 11a, 11b at each side of the opening11, irradiation of the sample material A may be carried out withoutoccurrence of collision of ions from the energy beam B with edges of theopening 11 of the sheet mesh 10. Thus, irradiation characteristics areenhanced and a higher quality sample material A may be obtained.Further, the tapered portion 11b allows smooth uniform flow of theenergy beam without turbulence and prevents a portion of the sheet mesh10 itself from being inadvertently irradiated in the vicinity of wherethe sample material A is placed. Thus, contamination of the samplematerial A by the material of the sheet mesh 10 is prevented.

FIGS. 5 to 9 show various alternative embodiments of a sheet meshutilized in the method of processing sample material for transmissionelectron microscopes according to the invention.

In FIG. 5, a alternative formation of a sheet mesh 10 is shown.According to this embodiment, an entire area between the upper edge 11aand the lower edge 11b of the opening 11 is taken up by the taperedportion 11c, that is, the untapered circumferential portion 11d is notpresent. According to this, more complete and defined irradiation of thesample material A is possible without occurrence of `shadowing` of theenergy beam B. As in the previous embodiment, the tapered portion 11c isat an angle corresponding to an irradiation angle of the energy beam B.

FIG. 6 shows a formation of the sheet mesh 10 in which the taperedportion 11c takes up the entire lower area of the sheet mesh 10. Thetaper angle may be formed lower than the angle of irradiation.

In FIG. 7, showing a further modification of the embodiment, an areabetween the upper edge 11a and the lower edge 11b of the opening 11 ofthe sheet mesh 10 is formed as a concave circumferential portion 11e forfurther assuring that interference does not occur between the energybeam B and the material of the sheet mesh 10.

Referring to FIG. 8, an entire lower area of the sheet mesh according tothis modification is formed as an outwardly curved portion 11f.

FIG. 9 shows an alternative formation of the sheet mesh 10 in which anupper surface 10a of the sheet mesh 10 is formed with a recessed portion11g, which may be of a size corresponding to that of the wafer of samplematerial A so as to assuredly hold the sample material A in place duringprocessing operations. The opening 11, the tapered portion 11c, etc.,may be formed as in the above-described first embodiment, or accordingto any of the modifications thereof.

Hereinbelow, a second embodiment of a sheet mesh utilized forpreparation of sample material A for processing according to the methodof the invention will be explained in detail referring to FIGS. 10 and11.

FIG. 10 shows a plan view of an upper (first) surface of a sheet mesh12. The elements off the sheet mesh 12 according to the presentembodiment include a circular opening 12a provided in a center portionof the sheet mesh 12, and a plurality of line portions 12b which areradially aligned with a center of the opening 12a. As can be seen inFIG. 11, opposing line portions 12b, 12b are aligned 180° apart suchthat, when the sample material A is placed over the opening 12a, theline of the membrane layer 2, which runs through the axial center of thewafer of sample material A as described above, aligns with an opposingtwo of the line portions 12b. Thus, according to the above arrangement,accurate placement of the membrane layer 2 across the center of theopening is assured. Thus misalignment of the membrane layer duringirradiation of the sample material, leading to formation of a defectivesample such as shown in FIG. 17(B), is prevented.

It will be noted that this sheet mesh is also applicable for processingof sample material prepared according to the conventional method shownin FIGS. 14(A) and 14(B). Also, as in the conventional process shown inFIG. 14(D), the sheet mesh 12 with the sample material A thereon may bemounted on a rotation apparatus 8 and rotated under vacuum conditionswhile being irradiated by the energy beam B.

According to the above described embodiment, and as shown in FIG. 12,optimal positioning of the membrane layer 2, the is, the portion of thesample material to be examined by the transmission electron microscope(not shown) is placed in the center of the irradiation opening 12aallowing the energy beam B to precisely irradiate the membrane layersfor providing samples of the highest quality. According to this, asingle membrane layer 2, or the center portion of the sample materialprepared according to the method of the invention, comprising anadhesion layer binding two facing membrane layers 2, 2, between twosubstrate layers 1, 1 may be also optimally positioned for obtaining themost favorable irradiation characteristics.

Referring now to FIG. 13, a perspective view of an alternativeconstruction of a sheet mesh according to the second embodiment is show.According to this, a sheet mesh 13 is provided with a central circularopening 13a, as with the previous embodiments. However, according to thepresent modification, on a first surface of the sheet mesh 13 on whichthe sample material A is to be placed, a recessed portion 13b is formed.That is, instead of the lines 12b of the previous embodiment, whichprovide visual means for positioning a membrane layer of the samplematerial, the present construction includes a recess determined at asize corresponding to that of the wafer of sample material A such thatthe sample material A is assuredly held in exactly the correct position.According to this, strict positioning of the membrane layer (or layers)is possible and displacement of the sample material A due to vibrationsor the like cannot occur.

Thus, according to the present invention, uniform irradiation of samplematerial A, for examination under a transmission electron microscope isprovided for creating high quality samples. The flow of the energy beamB irradiating the sample material A is not interfered with by portionsof the sheet mesh and contamination of the sample material by thematerial of the sheet mesh is avoided.

Further, according to the method of the invention, preparation of highquality samples of membrane layer material which it was not possible toprepare according to conventional methods may be created with thepresent method since a protection layer is provided between the membranelayers and an adhesion layer for preventing degradation of the membranelayer material during processing.

Also, according to the invention, precise positioning of the portion ofthe sample material to be examined is reliably established. That is, themembrane layers, allowing high quality samples to be reliably producedwithout occurrence of defects.

While the present invention has been disclosed in terms of the preferredembodiment in order to facilitate better understanding thereof, itshould be appreciated that the invention can be embodied in various wayswithout departing from the principle of the invention. Therefore, theinvention should be understood to include all possible embodiments andmodification to the shown embodiments which can be embodied withoutdeparting from the principle of the invention as set forth in theappended claims.

What is claimed is:
 1. A method for irradiation processing of laminatematerial used in a semiconductor device, comprising the stepsof:providing first and second substrates; applying a material layer toat least one surface of said first substrate and a material layer to atleast one surface of said second substrate; applying a protective layerover said material layer on said first substrate and a protective layerover said material layer on said second substrate; joining said materiallayer on said first substrate and said material layer on said secondsubstrate by joining each protective layer with an adhesion layer,thereby forming a laminate; cutting said laminate to a predetermineddimension such that said material layer on said first substrate, saidprotective layer on said material layer on said first substrate, saidadhesion layer, said protective layer on said material layer on saidsecond substrate, and said material layer on said second substratetogether define a line formed substantially through a center of the cutlaminate; forming an opening between first and second surfaces of asheet mesh; tapering edge portions of said opening between said firstand second surfaces at a predetermined irradiation angle; mounting saidlaminate over said opening on said first surface of said sheet mesh;irradiating said laminate via an energy beam at said irradiation anglethrough said opening in said sheet mesh.
 2. A method for irradiationprocessing as set forth in claim 1, further including a step, after saidtapering step, of forming a positioning recess in said first surface ofsaid sheet mesh said mounting step including inserting said laminate insaid recess.
 3. A method for irradiation processing as set forth inclaim 1, further including a step, after said tapering step, of markingsaid first surface of said sheet mesh with a positioning indication,said mounting step including aligning said laminate with saidpositioning indication.
 4. A method for irradiation processing as setforth in claim 1, wherein each material layer comprises Al.
 5. A methodfor irradiation processing as set forth in claim 1, wherein eachprotective layer comprises SiN.
 6. A method for irradiation processingas set forth in claim 5, wherein a thickness of each protective layer is500 nm.
 7. A method for irradiation processing as set forth in claim 1,wherein said energy beam is an argon ion beam.
 8. A method forirradiation processing as set forth in claim 1, wherein a plurality ofenergy beams are utilized for said irradiating step.
 9. A method forprocessing sample material for use with a transmission electronmicroscope, comprising the steps of:cutting a portion out of said samplematerial to be used with said transmission electron microscope; mountingsaid sample material on a first surface of a sheet mesh; providing anopening in said sheet mesh from said first surface to a second surfaceopposite said first surface, a gradient of an edge portion of saidopening being formed with a predetermined taper from said first surfaceto said second surface; and irradiating said sample material via anenergy beam directed through said opening in said sheet mesh; saidmethod further including a step of providing a recessed portion in saidfirst surface of said sheet mesh, said sheet mesh receiving said samplematerial in said recessed portion at said mounting step.
 10. A method asset forth in claim 9, wherein an axial direction of said energy beamduring said irradiation corresponds to an angle of said predeterminedtaper.
 11. A method as set forth in claim 9, further including a step ofrotating said sheet mesh during said irradiating step.
 12. A method asset forth in claim 9, wherein said energy beam is an argon ion beam. 13.A method as set forth in claim 9, wherein said irradiating step iscarried out by a plurality of energy beams.
 14. A sheet mesh for holdinga sample material for a transmission electron microscope, comprising:amesh having a substantially planar upper surface and a lower surface,the sample material being mountable in a position on said upper surface;a recess formed in said upper surface, said recess having a shapeconforming to the shape of the sample material whereby said samplematerial is held on said upper surface; a circular opening formedthrough a substantially center portion of said recess, said openingextending through said upper surface and said lower surface; whereinsaid mesh has a thickness which tapers off at an edge portion of saidcircular opening; and wherein said edge portion is contoured inwardtowards said lower surface.
 15. A sheet mesh for holding a samplematerial for a transmission electron microscope, comprising:a meshhaving a substantially planar upper surface and a lower surface, thesample material being mountable in a position on said upper surface; arecess formed in said upper surface, said recess having a shapeconforming to the shape of the sample material whereby said samplematerial is held on said upper surface; a circular opening formedthrough a substantially center portion of said recess, said openingextending through said upper surface and said lower surface; whereinsaid mesh has a thickness which tapers off at an edge portion of saidcircular opening; and wherein said edge portion is contoured outwardfrom said lower surface.